Centrifugal separator having a rotor body with a movable wall

ABSTRACT

The rotor of a centrifugal separator includes two axially separated end walls and one surrounding wall situated between the end walls. The end walls and a stack of separation discs within the rotor are maintained axially together by a central fastener. The surrounding wall, which is separate from the two end walls, is movable axially during rotor operation relative to at least one of the end walls. The surrounding wall has an inner diameter at the areas where it seals with the ends walls that is smaller than the portions between those sealing areas.

BACKGROUND OF THE INVENTION

The present invention relates to a centrifugal separator comprising arotor body which forms a separation chamber and comprises two axiallyseparated end walls and a surrounding wall situated axially between theend walls, a stack of conical separation discs arranged between the endwalls in the separation chamber coaxially with the rotor, and afastening means separate from the surrounding wall and arranged to keepthe end walls and the stack of separation discs therebetween axiallytogether. A centrifugal separator of this kind is described e.g. in U.S.Pat. No. 1,343,325.

As can be seen from U.S. Pat. No. 1,343,325 the two end walls of theknown centrifugal separator are kept axially together by means of acentral locking joint. This comprises a vertical column permanentlyconnected with the lower end wall and extending centrally through thecentrifuge rotor, and a looking ring threaded on to the column andretaining the upper end wall relative thereto. The surrounding wall ofthe rotor is formed in one piece with the upper end wall and is keptaxially in sealing engagement with the lower end wall by means of thecentral locking joint. Centrifugal separators of this kind were commonaround the turn of the century when the centrifuge rotors were stillrelatively small.

When larger centrifuge rotors were developed and higher rotationalspeeds were used the demands on strength of the central locking jointwere increased. As a consequence thereof another type of locking jointwas developed. One example of such a locking joint is shown in U.S. Pat.No. 1,571,943. This locking joint comprises a locking ring dimensionedand arranged to keep the rotor end walls axially together in the area ofthe largest peripheries thereof instead of, as previously, centrally inthe rotor. Thus, the locking ring has been given a substantially largerdiameter than before, whereby its threads may take up correspondinglylarger shearing forces.

A locking joint of the last mentioned type is more difficult to dealwith than a central locking joint and, therefore, is not desirable inconnection with relatively small centrifuge rotors.

SUMMARY OF THE INVENTION

The object of the present invention is, partly, to enable use of acentral locking joint in a centrifuge rotor of the kind here in questionand, partly, to make it possible to give such a centrifuge rotor arelatively large diameter and/or a relatively high rotational speedwithout overloading the central locking joint.

This object may be obtained according to the invention in a centrifugalseparator of the initially defined kind in a way such that thesurrounding wall is formed separate from both the end walls and arrangedto seal against them, that the surrounding wall has a smaller diameterin both the areas, in which it seals against the end walls, than it hasin an area axially between these areas, and that the surrounding wall isfree to move axially during rotor operation relative to at least one ofthe end walls in the area of its sealing thereagainst.

By this invention the rotor body may be given a relatively largediameter and/or be given a relatively high rotational speed without theaxial forces, by which the rotor body is loaded during rotor operationas a consequence of the overpressure of liquid rotating within therotor, loading to their full extent the end walls and the centralfastening means keeping these together. In other words, the surroundingwall of the rotor body may be shaped in a way such that it takes up, toa desired degree, oppositely directed axially forces from the liquidwithin the rotor, axial deformation of the rotor body being allowedduring operation thanks to the axial movability between the surroundingwall and at least one of the end walls.

In a preferred embodiment of the invention the surrounding wall hassubstantially the same inner diameter in both the areas in which itseals against the end walls, so that the whole axial pressure exerted byliquid within the rotor against the rotor body radially outside theouter edges of the end walls will be taken up by the surrounding wallduring operation of the rotor.

Thanks to the invention, centrifuge rotors having collecting spaces ofdifferent sizes radially outside the separation discs, e.g. forseparated solids, may be made of end walls and separation discs,respectively, of one and the same size. Only the surrounding walls haveto be produced in different sizes which, however, does not influence thesize of those forces loading the central locking joints of the rotorsduring their operation.

For simplifying manual cleaning of a centrifuge rotor according to theinvention from separated solids the separate surrounding wall preferablyis axially displaceable relative to both of the end walls, so that itcan be released from the other parts of the centrifuge rotor withoutneed of separating these parts. The surrounding wall can thus be axiallyseparated from the two end walls while these maintain by means of saidfastening means the stack of separation discs in position between theend walls. By giving the surrounding wall a larger diameter in anannular area axially between the areas, in which it is arranged to sealagainst the end walls, separated solids present in said annular area maybe removed from the rotor together with the surrounding wall without anyrisk of scraping them off against one of the end walls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a centrifugal separator showing a prior artconfiguration on the right-hand side and the instant invention on theleft-hand side.

FIG. 2 shows a particular embodiment of a structure for allowing limitedaxial movement of the surrounding wall of the centrifugal separatorrelative to the end wall.

DETAILED DESCRIPTION OF THE DRAWINGS

The drawing shows a centrifuge rotor intended for separation of smallsolids from a liquid. The centrifuge rotor is rotatable around avertical axis A. To the right of the rotational axis A there is shown arotor design of a previously known kind and to the left of therotational axis A there is shown a preferred embodiment of theinvention. In the following a centrifuge rotor designed according to theinvention is first described, after which a comparison is made betweenthis and a centrifuge rotor designed according to previously knowntechnique.

The centrifuge rotor according to the invention has a rotor bodycomprising a lower end wall 1, an upper end wall 2 and a surroundingwall 3 arranged axially between the end walls. The surrounding wall 3 isarranged to seal by means of annular gaskets 4 and 5 against therespective end walls 1 and 2 in a way such that a certain axial movementof the surrounding wall relative to the end walls is allowed undermaintained sealing axial movements of the surrounding wall 3 are limiteddownwardly by an annular flange 6 of the end wall 1 and upwardly by aring 7 threaded onto the radially outermost part of the end wall 2.

As can be seen from the drawing, the lower part of the surrounding wall3, that is sealing against the end wall 1, has a somewhat largerdiameter than the upper part of the surrounding wall 3 sealing againstthe end wall 2.

The upper end wall 2 has a central column 8 formed in one piecetherewith and extending axially downwardly towards and to abutmentagainst the lower end wall 1. The column 8 has the form of a hollowcylinder. A screw 9 is arranged to keep the column 8 and the lower endwall 1 axially together and to retain the whole rotor body on the upperpart of a vertical drive shaft 10.

Within the rotor body there is delimited a separation chamber 11 inwhich a stack of frusto-conical separation discs 12 is arrangedcoaxially with the rotor. The stack of separation discs rests on aconical partition 13 which in turn rests on the lower end wall 1.Between the end wall and the partition 13 there are delimited a numberof radial channels 14 distributed around the rotor axis A and formed bya groove in the end wall 1. The channels 14 communicate at theirradially outer ends with the separation chamber 11.

The hollow column 8 forms an inlet chamber 15 which via passages 16through the lower part of the column 8 communicates with the radiallyinner ends of the channels 14. A stationary inlet pipe 17 extendsaxially into the inlet chamber 15.

Radially between the column 8 and the inner edges of the separationdiscs 12 there is formed one annular channel or several axiallyextending channels 18. A number of through holes 19 in the upper endwall 2 communicate with the channels 18 and form an outlet of theseparation chamber for liquid separated therein.

The above described centrifuge rotor is intended to operate in thefollowing manner.

A liquid containing particles having a larger density than the liquid issupplied during rotor operation through the inlet pipe 17 into the inletchamber 15. Thence liquid is conducted through the channels 16 and 14into the separation chamber 11 and therein through the interspacesbetween the separation discs 12 radially inwardly.

In the separation chamber 11 the solid particles move as a consequenceof the centrifugal force radially outwardly, whereas liquid freed fromparticles flows radially inwardly and leaves the separation chamberthrough the axial channels 18 and the holes 19 in the end wall. Theholes 19 form so called overflow outlets from the separation chamber 11.

The solids are collected and deposit on the inside of the surroundingwall 3.

At a suitable point of time or when a certain amount of particles havedeposited on the surrounding wall 3 the supply of liquid through theinlet pipe 17 is interrupted and the rotor is stopped. After that theinlet pipe 17 and the ring 7 are removed, so that the surrounding wall 3can be lifted up and separated from the other parts of the rotor.

After the inside of the surrounding wall 3 has been cleaned fromseparated solids (sludge) the surrounding wall is again mounted on therotor and separation can be resumed. The separation discs 12 need not bedisassembled in connection with the cleaning operation.

In the upper part of the drawing figure there are shown two diagrams 20,21 and two vertical arrows 22, 23. The level of the free liquid surfaceformed in the separation chamber 11 during operation of the centrifugerotor, i.e. the radial level of the overflow outlets 19, is illustratedby two triangles 24, 25.

In the left diagram it is illustrated how the liquid pressure within theseparation chamber 11 grows radially outwardly from the level 24 of thefree liquid surface to a radial level 26, at which the lower part of thesurrounding wall 3 seals against the end wall 1. The arrow 22 thusillustrates the size of the axial liquid pressure acting on the rotorbody at the level 26.

The liquid pressure prevailing radially inside the level 26 acts axiallyagainst the two end walls 1 and 2 and thus causes an axial force whichhas to be taker up by the screw 9 for keeping the end walls axiallytogether. Radially outside the level 26 the liquid pressure in theseparation chamber 11 only acts on the surrounding wall 3, radially aswell as axially. Due to the fact that a certain axial movement isallowed by the axially outermost parts of the surrounding wall 3relative to the end walls 1 and 2 a certain elastic deformation of thesurrounding wall 3 as a consequence of the liquid pressure in theseparation chamber can be allowed without this causing a further load onthe screw 9. The axial forces to which the surrounding wall 3 issubjected by the liquid pressure radially outside the level 26 are thustaken up completely by the surrounding wall itself.

It is indicated by dotted lines that the surrounding wall 3 withunchanged dimensions in the areas in which it seals against the endwalls 1 and 2 may have different dimensions axially between these areas.Such a different shape of the surrounding wall 3 does not influence theaxial load to which the screw 9 will be subjected during operation ofthe centrifuge rotor. By use of the same end walls 1 and 2, the samestuck of separation discs 12 and the same screw 9 the centrifuge rotorthus may be provided with surrounding walls of different shape, allowingcollection of a larger or smaller amount of solids in the separationchamber.

To the right of the rotor axis A there is shown a rotor design of apreviously known kind. As can be seen in this case the upper end wall ofthe rotor body is formed in one piece with the surrounding wall of therotor body. Furthermore, the surrounding wall and the lower end wall areformed such that they seal against each other at the largest innerdiameter of the surrounding wall.

In this case, during rotor operation, each of the two end walls will besubjected to an axial liquid pressure all the way from the level 25 ofthe free liquid surface in the separation chamber and out to theradially outermost part of the separation chamber. The arrow 23illustrates the size of the liquid pressure in the radially outermostpart of the separation chamber.

This means that a member keeping the rotor body together--such as thescrew 9--will be loaded by a substantially larger axial force in a rotordesign of the previously known kind (to the right in the drawing) thanin a rotor design according to the invention (to the left in thedrawing).

Irrespective of the kind of central means used for keeping the rotorbody axially together the invention thus brings with it an advantageconcerning the dimensioning of this means. The invention is particularlyadvantageous if the means in question has to be made very small forvarious reasons, e.g. as shown in the drawing in the form of a screwhaving a small diameter and being threaded into the end portion of athin drive shaft.

In the above described embodiment of the invention a locking ring 7 hasbeen used as a means for limiting axial movement of the surrounding wall3 upwardly during rotor operation. Other more simple means doing thesame thing can of course be used. Particularly, if the surrounding wallhas substantially the same inner diameter in both of the areas in whichit seals against the end walls 1 and 2, said means for limiting theaxial movement of the surrounding wall may be made very simple, since inthis case they will not be subjected to any substantial axial load fromthe surrounding wall 3 during rotor operation.

If desired, said means, e.g. the locking ring 7, may be produced in onepiece with the surrounding wall 3, since the rotor design according tothe invention only presumes that the surrounding wall 3 has an axialmovability relative to one of the end walls.

FIG. 2 shows a particular embodiment of said means for limiting theaxial movement of the surrounding wall 3a relative to the end wall 2a.Here use has been made of an annular gasket 5a, preferably made ofrubber or some other elastic material, which during operation of thecentrifuge rotor is allowed to expand radially outwardly--influenced bythe centrifugal force--from a position in a first annular groove formedin a radially outward directed surface of the end wall 2a partly into asecond annular groove formed in a radially inward facing surface of thesurrounding wall 3a.

As long as the centrifuge rotor does not rotate, the gasket 5a thus willbe retained in its groove in the end wall 2a, in which it admits freeaxial movement of the surrounding wall 3a relative to the end wall 2a,but during operation of the centrifuge rotor the gasket 5a will be in aradially expanded state in a position as illustrated in FIG. 2. In thelatter position it allows a certain small axial movement of thesurrounding; wall 3a relative to the end wall 2a, but the surroundingwall 3a can not remove itself completely from the end wall 2a withoutthe gasket 5a being sheared to pieces.

We claim:
 1. A centrifugal separator comprising: a rotor body rotatableabout an axis and forming a separation chamber, the rotor bodycomprising two axially separated end walls and a surrounding wallsituated axially between the end walls; a stack of conical separationdiscs arranged between the end walls in the separation chamber andcoaxially with the rotor; and fastening means arranged to keep the endwalls and the stack of separation discs axially together, thesurrounding wall being formed separate from the fastening means and theend walls and being sealed at two respective areas against the endwalls, the surrounding wall further having a smaller inner diameter inboth of said areas in which it seals against the end walls that it hasin an area axially between these said areas, and the surrounding wallduring rotor operation bring free to move axially relative to at leastone of the end walls in the area of its sealing thereagainst.
 2. Acentrifugal separator according to claim 1 wherein the surrounding wallhas substantially the same inner diameter in both of the areas in whichit seals against the end walls.
 3. A centrifugal separator according toclaim 2, wherein the surrounding wall is releasable from both said endwalls by being axially displaceable relative thereto when thecentrifugal separator is out of operation.
 4. A centrifugal separatoraccording to claim 3, wherein the separation discs are frusto-conicaland have radially inner and radially outer edges, and said fasteningmeans extends between the end walls radially inside the inner edges ofthe separation discs.
 5. A centrifugal separator according to claim 2,wherein the separation discs are frusto-conical and have radially innerand radially outer edges, and said fastening means extends between theend walls radially inside the inner edges of the separation discs.
 6. Acentrifugal separator according to claim 2, wherein said fastening meanscomprises at least one first member that is permanently connected withone said end wall and extends axially through the stack of separationdiscs, and one releasable second member arranged to removably connectanother one of said end walls with the first member.
 7. A centrifugalseparator according to claim 1, wherein the rotor body is supported by adrive shaft that is connected with one said end wall, and thesurrounding wall has a larger inner diameter in the area of its sealingagainst said end wall than in the area of its sealing against anotherone of said end walls.
 8. A centrifugal separator according to claim 7,wherein the surrounding wall is releasable from both said end walls bybeing axially displaceable relative thereto when the centrifugalseparator is out of operation.
 9. A centrifugal separator according toclaim 8, wherein the separation discs are frusto-conical and haveradially inner and radially outer edges, and said fastening meansextends between the end walls radially inside the inner edge of theseparation discs.
 10. A centrifugal separator according to claim 7,wherein the separation discs are frusto-conical and have radially innerand radially outer edges, and said fastening means extends between theend walls radially inside the inner edges of the separation discs.
 11. Acentrifugal separator according to claim 7, wherein said fastening meanscomprises at least one first member that is permanently connected withone said end wall and extends axially through the stack of separationdiscs, and one releasable second member arranged to removably connectanother one of said end walls with the first member.
 12. A centrifugalseparator according to claim 1, wherein the surrounding wall isreleasable from both said end walls by being axially displaceablerelative thereto when the centrifugal separator is out of operation. 13.A centrifugal separator according to claim 12, wherein the separationdiscs are frusto-conical and have radially inner and radially outeredges, and said fastening means extends between the end walls radiallyinside the inner edges of the separation discs.
 14. A centrifugalseparator according to claim 12, wherein said fastening means compriseat least one first member that is permanently connected with one saidend wall and extends axially through the stack of separation discs andone releasable second member arranged to removably connect another oneof said end walls with the first member.
 15. A centrifugal separatoraccording to claim 1, wherein the separation discs are frusto-conicaland have radially inner and radially outer edges, and said fasteningmeans extends between the end walls radially inside the inner edges ofthe separation discs.
 16. A centrifugal separator according to claim 15,wherein said fastening means comprises at least one first member that ispermanently connected with one said end wall and extends axially throughthe stack of separation discs, and one releasable second member arrangedto removably connect another one of said end walls with the firstmember.
 17. A centrifugal separator according to claim 1, wherein saidfastening means comprises at least one first member that is permanentlyconnected with one said end wall and extends axially through the stackof separation discs, and one releasable second member arranged toremovably connect another one of said end walls with the first member.18. A centrifugal separator according to claim 17, wherein the rotorbody is supported by a vertical driving shaft and said releasable secondmember comprises a screw that is threaded into an axial hole in thedriving shaft for retaining the rotor body thereon.